Enanta Pharmaceuticals (ENTA) 10-Q 9 May 22 2022 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2022	Apr. 27, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Trading Symbol	ENTA
Entity Registrant Name	ENANTA PHARMACEUTICALS, INC
Entity Central Index Key	0001177648
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-35839
Security Exchange Name	NASDAQ
Entity Tax Identification Number	04-3205099
Entity Address, Address Line One	500 Arsenal Street
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	617
Title of 12(b) Security	Common Stock, par value $0.01 per share
Local Phone Number	607-0800
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		20,712,691

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Current assets:
Cash and cash equivalents	$ 40,989	$ 57,206
Short-term marketable securities	239,338	186,796
Accounts receivable	18,716	23,576
Prepaid expenses and other current assets	14,078	14,188
Income tax receivable	28,748	37,255
Total current assets	341,869	319,021
Long-term marketable securities	42,218	108,416
Property and equipment, net	4,815	5,943
Operating lease, right-of-use assets	17,216	4,711
Restricted cash	608	608
Other long-term assets	92	92
Total assets	406,818	438,791
Current liabilities:
Accounts payable	5,985	9,540
Accrued expenses and other current liabilities	21,740	22,429
Operating lease liabilities	3,013	4,203
Total current liabilities	30,738	36,172
Operating lease liabilities, net of current portion	15,115	1,126
Series 1 nonconvertible preferred stock	1,506	1,506
Other long-term liabilities	876	558
Total liabilities	48,235	39,362
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock; $0.01 par value per share, 100,000 shares authorized; 20,618 and 20,238 shares issued and outstanding at March 31, 2022 and September 30, 2021, respectively	206	202
Additional paid-in capital	376,545	351,033
Accumulated other comprehensive loss	(3,037)	(382)
(Accumulated deficit) retained earnings	(15,131)	48,576
Total stockholders' equity	358,583	399,429
Total liabilities and stockholders' equity	$ 406,818	$ 438,791

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Thousands	Mar. 31, 2022	Sep. 30, 2021
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	20,618	20,238
Common stock, shares outstanding	20,618	20,238

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Royalty revenue	$ 18,716,000	$ 20,132,000	$ 46,364,000	$ 51,875,000
Type Of Revenue Extensible List	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember
Operating expenses:
Research and development	$ 42,087,000	$ 41,506,000	$ 90,636,000	$ 78,171,000
General and administrative	10,476,000	8,326,000	19,984,000	15,703,000
Total operating expenses	52,563,000	49,832,000	110,620,000	93,874,000
Loss from operations	(33,847,000)	(29,700,000)	(64,256,000)	(41,999,000)
Other income:
Other income, net	255,000	545,000	549,000	1,222,000
Total other income, net	255,000	545,000	549,000	1,222,000
Loss before income taxes	(33,592,000)	(29,155,000)	(63,707,000)	(40,777,000)
Income tax benefit	0	(7,110,000)	0	(10,404,000)
Net loss	$ (33,592,000)	$ (22,045,000)	$ (63,707,000)	$ (30,373,000)
Net loss per share:
Basic	$ (1.63)	$ (1.09)	$ (3.11)	$ (1.51)
Diluted	$ (1.63)	$ (1.09)	$ (3.11)	$ (1.51)
Weighted average shares outstanding:
Basic	20,551	20,171	20,473	20,131
Diluted	20,551	20,171	20,473	20,131

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (33,592)	$ (22,045)	$ (63,707)	$ (30,373)
Other comprehensive loss:
Net unrealized losses on marketable securities	(2,031)	(350)	(2,655)	(789)
Total other comprehensive loss	(2,031)	(350)	(2,655)	(789)
Comprehensive loss	$ (35,623)	$ (22,395)	$ (66,362)	$ (31,162)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	(Accumulated Deficit) Retained Earnings [Member]
Beginning Balance at Sep. 30, 2020	$ 455,580	$ 201	$ 326,963	$ 844	$ 127,572
Beginning Balance, Shares at Sep. 30, 2020		20,077
Exercise of stock options	833		833
Exercise of stock options, Shares		33
Vesting of restricted stock units, net of withholding, Shares		32
Vesting of restricted stock units, net of withholding	(534)		(534)
Stock-based compensation expense	4,883		4,883
Other comprehensive loss	(439)			439
Net Income (loss)	(8,328)				(8,328)
Ending Balance at Dec. 31, 2020	451,995	$ 201	332,145	405	119,244
Ending Balance, Shares at Dec. 31, 2020		20,142
Beginning Balance at Sep. 30, 2020	455,580	$ 201	326,963	844	127,572
Beginning Balance, Shares at Sep. 30, 2020		20,077
Other comprehensive loss	(789)
Net Income (loss)	(30,373)
Ending Balance at Mar. 31, 2021	436,032	$ 202	338,576	55	97,199
Ending Balance, Shares at Mar. 31, 2021		20,185
Beginning Balance at Dec. 31, 2020	451,995	$ 201	332,145	405	119,244
Beginning Balance, Shares at Dec. 31, 2020		20,142
Exercise of stock options	1,152	$ 1	1,151
Exercise of stock options, Shares		43
Stock-based compensation expense	5,280		5,280
Other comprehensive loss	(350)			350
Net Income (loss)	(22,045)				(22,045)
Ending Balance at Mar. 31, 2021	436,032	$ 202	338,576	55	97,199
Ending Balance, Shares at Mar. 31, 2021		20,185
Beginning Balance at Sep. 30, 2021	399,429	$ 202	351,033	(382)	48,576
Beginning Balance, Shares at Sep. 30, 2021		20,238
Exercise of stock options	10,409	$ 2	10,407
Exercise of stock options, Shares		248
Vesting of restricted stock units, net of withholding, Shares		20
Vesting of restricted stock units, net of withholding	(777)	$ 1	(778)
Stock-based compensation expense	6,062		6,062
Other comprehensive loss	(624)			624
Net Income (loss)	(30,115)				(30,115)
Ending Balance at Dec. 31, 2021	384,384	$ 205	366,724	(1,006)	18,461
Ending Balance, Shares at Dec. 31, 2021		20,506
Beginning Balance at Sep. 30, 2021	$ 399,429	$ 202	351,033	(382)	48,576
Beginning Balance, Shares at Sep. 30, 2021		20,238
Exercise of stock options, Shares	345
Other comprehensive loss	$ (2,655)
Net Income (loss)	(63,707)
Ending Balance at Mar. 31, 2022	358,583	$ 206	376,545	(3,037)	(15,131)
Ending Balance, Shares at Mar. 31, 2022		20,618
Beginning Balance at Dec. 31, 2021	384,384	$ 205	366,724	(1,006)	18,461
Beginning Balance, Shares at Dec. 31, 2021		20,506
Exercise of stock options	3,802	$ 1	3,801
Exercise of stock options, Shares		97
Vesting of restricted stock units, net of withholding, Shares		15
Vesting of restricted stock units, net of withholding	(451)		(451)
Stock-based compensation expense	6,471		6,471
Other comprehensive loss	(2,031)			(2,031)
Net Income (loss)	(33,592)				(33,592)
Ending Balance at Mar. 31, 2022	$ 358,583	$ 206	$ 376,545	$ (3,037)	$ (15,131)
Ending Balance, Shares at Mar. 31, 2022		20,618

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities
Net loss	$ (63,707)	$ (30,373)
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	12,533	10,163
Depreciation and amortization expense	1,602	1,705
Premium paid on marketable securities	(802)	(1,238)
Amortization of premium on marketable securities	928	956
Change in operating assets and liabilities:
Accounts receivable	4,860	3,360
Prepaid expenses and other current assets	110	(5,444)
Income tax receivable	8,507	0
Operating lease, right-of-use assets	2,784	2,565
Accounts payable	(3,473)	15
Accrued expenses	(808)	1,703
Operating lease liabilities	(2,498)	(2,797)
Other long-term liabilities	318	(84)
Net cash used in operating activities	(39,646)	(19,469)
Cash flows from investing activities
Purchase of marketable securities	(124,631)	(171,586)
Proceeds from maturities and sale of marketable securities	135,514	179,917
Purchase of property and equipment	(437)	(318)
Net cash provided by investing activities	10,446	8,013
Cash flows from financing activities
Proceeds from exercise of stock options	14,211	1,985
Payments for settlement of share-based awards	(1,228)	(534)
Net cash provided by financing activities	12,983	1,451
Net decrease in cash, cash equivalents and restricted cash	(16,217)	(10,005)
Cash, cash equivalents and restricted cash at beginning of period	57,814	87,739
Cash, cash equivalents and restricted cash at end of period	41,597	77,734
Supplemental disclosure of non-cash operating and investing information:
Purchases of fixed assets included in accounts payable and accrued expenses	174	17
Operating lease liabilities arising from obtaining right-of-use assets	$ 15,559	$ 2,517

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Mar. 31, 2022
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Enanta Pharmaceuticals, Inc. (the “Company”), incorporated in Delaware in 1995 , is a biotechnology company that uses its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs for the treatment of viral infections and liver diseases. The Company discovered glecaprevir, the second of two protease inhibitors discovered and developed through its collaboration with AbbVie for the treatment of chronic hepatitis C virus, or HCV. Glecaprevir is co-formulated as part of AbbVie’s leading direct-acting antiviral, or DAA, combination treatment for HCV, which is marketed under the tradenames MAVYRET® (U.S.) and MAVIRET®(ex-U.S.) (glecaprevir/pibrentasvir). Royalties from the Company’s AbbVie collaboration and its existing financial resources provide funding to support the Company’s wholly-owned research and development programs, which are primarily focused on the following disease targets: respiratory syncytial virus (“RSV”), hepatitis B virus (“HBV”), SARS-CoV-2, and human metapneumovirus (“hMPV”). The Company is subject to many of the risks common to companies in the biotechnology industry, including but not limited to, the uncertainties of research and development, competition from technological innovations of others, dependence on collaborative arrangements, protection of proprietary technology, dependence on key personnel and compliance with government regulation. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approvals, prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure, and extensive compliance reporting capabilities. COVID-19 In March 2020, the World Health Organization declared COVID-19 a global pandemic and countries worldwide implemented various measures to contain the spread of the SARS-CoV-2 virus. National, state and local governments in affected regions have implemented and may continue to implement varying safety precautions, including quarantines, border closures, increased border controls, travel restrictions, shelter-in-place orders and shutdowns, business closures, cancellations of public gatherings and other measures. The extent and severity of the impact on the Company’s business and clinical trials will be determined largely by the extent to which there are disruptions in the supply chains for its research and product candidates, delays in the conduct of ongoing and future clinical trials, or reductions in the number of patients accessing AbbVie’s HCV regimens, or any combination of those events. During the second half of fiscal 2021 and through March 31, 2022 , AbbVie experienced a decline in HCV sales compared to prior years as a result of a reduction in patients accessing AbbVie’s HCV regimens due to the COVID-19 pandemic. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition will depend on future developments that are highly uncertain and cannot be accurately predicted, including new information that may emerge concerning COVID-19 and its variants and public health actions taken to contain it, as well as the cumulative economic impact of both of those factors. Unaudited Interim Financial Information The consolidated balance sheet at September 30, 2021 was derived from audited financial statements but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying unaudited consolidated financial statements as of March 31, 2022 and for the three and six months ended March 31, 2022 and 2021 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended September 30, 2021. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of March 31, 2022 and results of operations for the three and six months ended March 31, 2022 and 2021 and cash flows for the six months ended March 31, 2022 and 2021 have been made. The results of operations for the three and six months ended March 31, 2022 are not necessarily indicative of the results of operations that may be expected for subsequent quarters or the year ending September 30, 2022. The accompanying consolidated financial statements have been prepared in conformity with GAAP. All amounts in the consolidated financial statements and in the notes to the consolidated financial statements, except per share amounts, are in thousands unless otherwise indicated.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies For the Company’s Significant Accounting Policies, please refer to its Annual Report on Form 10-K for the fiscal year ended September 30, 2021. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, management’s judgments with respect to its revenue arrangements; valuation of stock-based awards and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. The future developments of the COVID-19 pandemic also may directly or indirectly impact the Company’s business. The Company has made estimates of the impact of COVID-19 in the Company’s consolidated financial statements as of March 31, 2022 . Actual results could differ from the Company’s estimates. Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) , which removes certain exceptions to the general principles in Topic 740 – Income Taxes and improves consistent application of and simplifies GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This ASU became effective for the Company beginning October 1, 2021 and interim periods within that year. The adoption of the standard did not have a material impact on the Company's financial position or results of operations. Recently Issued Accounting Pronouncements Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	6 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities that were subject to fair value measurement on a recurring basis as of March 31, 2022 and September 30, 2021, and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at March 31, 2022 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 36,356 $ — $ — $ 36,356 Marketable securities: U.S. Treasury notes 106,992 — — 106,992 Corporate bonds — 108,190 — 108,190 Commercial paper — 66,374 — 66,374 $ 143,348 $ 174,564 $ — $ 317,912 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,506 $ 1,506 $ — $ — $ 1,506 $ 1,506 Fair Value Measurements at September 30, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 54,819 $ — $ — $ 54,819 Marketable securities: U.S. Treasury notes 83,038 — — 83,038 Corporate bonds — 124,703 — 124,703 Commercial paper — 87,471 — 87,471 $ 137,857 $ 212,174 $ — $ 350,031 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,506 1,506 $ — $ — $ 1,506 $ 1,506 During the six months ended March 31, 2022 and 2021 , there were no transfers between Level 1, Level 2 and Level 3. The outstanding shares of Series 1 nonconvertible preferred stock are measured at fair value. The fair value of these instruments was based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The Company utilized a probability-weighted valuation model which takes into consideration various outcomes that may require the Company to transfer assets upon liquidation. Changes in the fair value of the Series 1 nonconvertible preferred stock are recognized in other income (expense), net in the consolidated statements of operations. The recurring Level 3 fair value measurements of the Company’s outstanding Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range March 31, September 30, Unobservable Input 2022 2021 Probabilities of payout 0 %- 65 % 0 %- 65 % Discount rate 4.25 % 4.25 % The following table provides a rollforward of the aggregate fair values of the Company’s outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Series 1 Balance, September 30, 2021 $ 1,506 Change in fair value of nonconvertible preferred stock — Balance, March 31, 2022 $ 1,506

Marketable Securities

Marketable Securities	6 Months Ended
	Mar. 31, 2022
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of March 31, 2022 and September 30, 2021, the fair value of available-for-sale marketable securities, by type of security, was as follows: March 31, 2022 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 109,901 $ 3 $ ( 1,714 ) $ — $ 108,190 U.S. Treasury notes 107,934 3 ( 945 ) — 106,992 Commercial paper 66,374 — — — 66,374 $ 284,209 $ 6 $ ( 2,659 ) $ — $ 281,556 September 30, 2021 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 124,678 $ 93 $ ( 68 ) $ — $ 124,703 Commercial paper 87,471 — — — 87,471 U.S. Treasury notes 83,061 3 ( 26 ) — 83,038 $ 295,210 $ 96 $ ( 94 ) $ — $ 295,212 As of March 31, 2022 and September 30, 2021 , marketable securities consisted of investments that mature within one year , with the exception of certain corporate bonds and U.S. Treasury notes, which have maturities between one and three years and an aggregate fair value of $ 42,218 and $ 108,416 , respectively.

Accrued Expenses and Other Long

Accrued Expenses and Other Long-Term Liabilities	6 Months Ended
	Mar. 31, 2022
Payables And Accruals [Abstract]
Accrued Expenses and Other Long-Term Liabilities	5. Accrued Expenses and Other Long-Term Liabilities Accrued expenses and other current liabilities, as well as other long-term liabilities, consisted of the following as of March 31, 2022 and September 30, 2021: March 31, September 30, 2022 2021 (in thousands) Accrued expenses: Accrued pharmaceutical drug manufacturing $ 14,412 $ 8,402 Accrued research and development expenses 2,616 6,062 Accrued payroll and related expenses 2,960 6,094 Accrued professional fees 633 700 Accrued other 1,119 1,171 $ 21,740 $ 22,429 Other long-term liabilities: Uncertain tax positions $ 530 $ 558 Asset retirement obligation 346 — $ 876 $ 558

AbbVie Collaboration

AbbVie Collaboration	6 Months Ended
	Mar. 31, 2022
Organization Consolidation And Presentation Of Financial Statements [Abstract]
AbbVie Collaboration	6. AbbVie Collaboration The Company has a Collaborative Development and License Agreement (as amended, the “AbbVie Agreement”), with AbbVie to identify, develop and commercialize HCV NS3 and NS3/4A protease inhibitor compounds, including paritaprevir and glecaprevir, under which the Company has received license payments, proceeds from a sale of preferred stock, research funding payments, milestone payments and royalties totaling approximately $ 1,169,000 through March 31, 2022. Since the Company satisfied all of its performance obligations under the AbbVie Agreement by the end of fiscal 2011, all milestone payments received since then have been recognized as revenue when the milestones were achieved by AbbVie. The Company is receiving annually tiered royalties per Company protease product ranging from ten percent up to twenty percent, or on a blended basis from ten percent up to the high teens, on the portion of AbbVie’s calendar year net sales of each HCV regimen that is allocated to the protease inhibitor in the regimen. Beginning with each January 1, the cumulative net sales of a given royalty-bearing protease inhibitor product start at zero for purposes of calculating the tiered royalties on a product-by-product basis.

Series 1 Nonconvertible Preferr

Series 1 Nonconvertible Preferred Stock	6 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
Series 1 Nonconvertible Preferred Stock	7. Series 1 Nonconvertible Preferred Stock As of March 31, 2022 , 1,930 shares of Series 1 nonconvertible preferred stock were issued and outstanding. Since these shares qualify as a derivative, the outstanding shares are carried at fair value as a liability on the Company’s consolidated balance sheet.

Stock-Based Awards

Stock-Based Awards	6 Months Ended
	Mar. 31, 2022
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	8. Stock-Based Awards The Company grants stock-based awards, including stock options, restricted stock units and other unit awards under its 2019 Equity Incentive Plan (the “2019 Plan”), which was approved by its stockholders on February 28, 2019 and amended in March 2021 and March 2022. The Company also has outstanding stock option awards under its 2012 Equity Incentive Plan (the “2012 Plan”) and its amended and restated 1995 Equity Incentive Plan (the “1995 Plan”), but is no longer granting awards under these plans. The following table summarizes stock option activity, including performance-based options, for the year-to-date period ending March 31, 2022: Shares Weighted Weighted Aggregate (in thousands) (in years) (in thousands) Outstanding as of September 30, 2021 3,852 $ 48.61 6.4 $ 49,173 Granted 713 73.82 Exercised ( 345 ) 41.26 Forfeited ( 96 ) 67.91 Outstanding as of March 31, 2022 4,124 $ 53.13 6.7 $ 82,997 Options vested and expected to vest as of 4,124 $ 53.13 6.7 $ 82,997 Options exercisable as of March 31, 2022 2,496 $ 47.87 5.2 $ 63,476 Market and Performance-Based Stock Unit Awards The Company awards both performance share units, or PSUs, and relative total stockholder return units, or rTSRUs, to its executive officers. The number of units granted represents the target number of shares of common stock that may be earned; however, the actual number of shares that may be earned ranges from 0 % to 150 % of the target number. The number of shares cancelled represents the target number of shares, less any shares that vested. The following table summarizes PSU and rTSRU activity for the year-to-date period ending March 31, 2022: PSUs rTSRUs Shares Weighted Shares Weighted (in thousands, except per share data) Unvested at September 30, 2021 111 $ 49.31 111 $ 31.26 Granted 33 77.39 33 54.80 Vested ( 5 ) 61.59 ( 18 ) 40.13 Cancelled ( 27 ) 61.59 ( 14 ) 40.13 Unvested at March 31, 2022 112 54.01 112 $ 35.59 Restricted Stock Units The following table summarizes the restricted stock unit activity for the year-to-date period ending March 31, 2022: Restricted Stock Weighted (in thousands, except per share data) Unvested at September 30, 2021 117 $ 43.57 Granted 138 75.33 Vested ( 29 ) 43.57 Cancelled ( 9 ) 57.19 Unvested at March 31, 2022 217 $ 63.15 Stock-Based Compensation Expense During the three and six months ended March 31, 2022 and 2021 the Company recognized the following stock-based compensation expense: Three Months Ended Six Months Ended March 31, March 31, 2022 2021 2022 2021 (in thousands) Research and development $ 2,710 $ 2,536 $ 5,294 $ 4,955 General and administrative 3,761 2,744 7,239 5,208 $ 6,471 $ 5,280 $ 12,533 $ 10,163 Three Months Ended Six Months Ended March 31, March 31, 2022 2021 2022 2021 (in thousands) Stock options $ 4,962 $ 4,514 $ 9,710 $ 8,863 Performance stock units 79 — 512 — rTSRUs 531 444 823 721 Restricted stock units 899 322 1,488 579 $ 6,471 $ 5,280 $ 12,533 $ 10,163 During the three and six months ended March 31, 2022, the Company recognized stock-based compensation expense for performance-based stock units for which vesting became probable upon achievement of performance-based targets that occurred during the performance period. As of March 31, 2022, the Company had an aggregate of $ 66,162 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.9 years.

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three and six months ended March 31, 2022 and 2021: Three Months Ended Six Months Ended March 31, March 31, 2022 2021 2022 2021 (in thousands, except per share data) Basic net loss per share: Numerator: Net loss $ ( 33,592 ) $ ( 22,045 ) $ ( 63,707 ) $ ( 30,373 ) Denominator: Weighted average common shares outstanding 20,551 20,171 20,473 20,131 Net loss per share common share—basic $ ( 1.63 ) $ ( 1.09 ) $ ( 3.11 ) $ ( 1.51 ) Diluted net loss per share: Numerator: Net loss $ ( 33,592 ) $ ( 22,045 ) $ ( 63,707 ) $ ( 30,373 ) Denominator: Weighted average common shares outstanding 20,551 20,171 20,473 20,131 Dilutive effect of common stock equivalents — — — — Weighted average common shares outstanding 20,551 20,171 20,473 20,131 Net loss per share common share—diluted $ ( 1.63 ) $ ( 1.09 ) $ ( 3.11 ) $ ( 1.51 ) Anti-dilutive common stock equivalents excluded 3,699 4,268 3,267 4,307 The impact of certain common stock equivalents was excluded from the computation of diluted net loss per share for the periods in which the Company incurred a net loss since the impact of such common stock equivalents would have been anti-dilutive.

Income Taxes

Income Taxes	6 Months Ended
	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes For the three and six months ended March 31, 2022 , the Company recorded no income tax expense due to its expected fiscal 2022 loss which it is not able to carryback. For the three and six months ended March 31, 2021, the Company recorded an income tax benefit of $ 7,110 and $ 10,404 , respectively, due to the Company’s ability and intent to carryback its 2021 fiscal year tax loss under the Coronavirus Aid, Relief and Economic Security Act (the “ CARES Act”), which was signed into law in March 2020 . As of March 31, 2022, the Company recorded an income tax receivable of $ 28,748 consisting of an estimated federal net operating loss carryback for fiscal 2021 for which the Company will request a refund in the future. As of March 31, 2022, the Company has recorded a valuation allowance against all of its net deferred tax assets. The Company continues to believe it more likely that it will not have sufficient taxable income in the future that will allow it to realize all of its existing deferred tax assets. This is due to the fact the Company’s expenses are increasing as it continues to progress its wholly-owned research and development programs, while its royalty revenues from the AbbVie Agreement are not increasing.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 31, 2022
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Litigation and Contingencies Related to Use of Intellectual Property From time to time, the Company may become subject to legal proceedings, claims and litigation arising in the ordinary course of business. The Company currently is not a party to any litigation. However, third parties might allege that the Company or its collaborators are infringing their patent rights or that the Company is otherwise violating their intellectual property rights. Such third parties may resort to litigation against the Company or its collaborators, which the Company has agreed to indemnify. With respect to some of these patents, the Company expects that it will be required to obtain licenses and could be required to pay license fees or royalties, or both. These licenses may not be available on acceptable terms, or at all. A costly license, or inability to obtain a necessary license, would have a material adverse effect on the Company’s financial condition, results of operations or cash flows. The Company accrues contingent liabilities when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. Indemnification Agreements In the ordinary course of business, the Company may provide indemnifications of varying scope and terms to customers, vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from services to be provided to the Company, or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. In addition, the Company maintains officers and directors insurance coverage. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its financial statements as of March 31, 2022.

Leases

Leases	6 Months Ended
	Mar. 31, 2022
Leases [Abstract]
Leases	12. Leases On November 19, 2021, the Company exercised its option to extend the lease term of its existing office and laboratory space at 500 Arsenal Street for an additional 5 years through September 1, 2027. The Company accounted for the extension as a modification and re-assessed the classification of the lease as an operating lease. The total remeasurement of the lease resulted in an increase in the right of use asset and lease liability of $ 15,048 . The updated minimum lease payments related to the 500 Arsenal Street lease as a result of the extension totaled $ 20,342 .

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, management’s judgments with respect to its revenue arrangements; valuation of stock-based awards and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. The future developments of the COVID-19 pandemic also may directly or indirectly impact the Company’s business. The Company has made estimates of the impact of COVID-19 in the Company’s consolidated financial statements as of March 31, 2022 . Actual results could differ from the Company’s estimates.
Recently Adopted and Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) , which removes certain exceptions to the general principles in Topic 740 – Income Taxes and improves consistent application of and simplifies GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This ASU became effective for the Company beginning October 1, 2021 and interim periods within that year. The adoption of the standard did not have a material impact on the Company's financial position or results of operations. Recently Issued Accounting Pronouncements Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	6 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities that were subject to fair value measurement on a recurring basis as of March 31, 2022 and September 30, 2021, and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at March 31, 2022 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 36,356 $ — $ — $ 36,356 Marketable securities: U.S. Treasury notes 106,992 — — 106,992 Corporate bonds — 108,190 — 108,190 Commercial paper — 66,374 — 66,374 $ 143,348 $ 174,564 $ — $ 317,912 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,506 $ 1,506 $ — $ — $ 1,506 $ 1,506 Fair Value Measurements at September 30, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 54,819 $ — $ — $ 54,819 Marketable securities: U.S. Treasury notes 83,038 — — 83,038 Corporate bonds — 124,703 — 124,703 Commercial paper — 87,471 — 87,471 $ 137,857 $ 212,174 $ — $ 350,031 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,506 1,506 $ — $ — $ 1,506 $ 1,506
Fair Value Measurements of the Company's Outstanding Series 1 Nonconvertible Preferred Stock	The recurring Level 3 fair value measurements of the Company’s outstanding Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range March 31, September 30, Unobservable Input 2022 2021 Probabilities of payout 0 %- 65 % 0 %- 65 % Discount rate 4.25 % 4.25 %
Rollforward of Aggregate Fair Values of Outstanding Series 1 Nonconvertible Preferred Stock	The following table provides a rollforward of the aggregate fair values of the Company’s outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Series 1 Balance, September 30, 2021 $ 1,506 Change in fair value of nonconvertible preferred stock — Balance, March 31, 2022 $ 1,506

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Mar. 31, 2022
Investments Debt And Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of March 31, 2022 and September 30, 2021, the fair value of available-for-sale marketable securities, by type of security, was as follows: March 31, 2022 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 109,901 $ 3 $ ( 1,714 ) $ — $ 108,190 U.S. Treasury notes 107,934 3 ( 945 ) — 106,992 Commercial paper 66,374 — — — 66,374 $ 284,209 $ 6 $ ( 2,659 ) $ — $ 281,556 September 30, 2021 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 124,678 $ 93 $ ( 68 ) $ — $ 124,703 Commercial paper 87,471 — — — 87,471 U.S. Treasury notes 83,061 3 ( 26 ) — 83,038 $ 295,210 $ 96 $ ( 94 ) $ — $ 295,212

Accrued Expenses and Other Lo_2

Accrued Expenses and Other Long-Term Liabilities (Tables)	6 Months Ended
	Mar. 31, 2022
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities as well as Other Long-Term Liabilities	Accrued expenses and other current liabilities, as well as other long-term liabilities, consisted of the following as of March 31, 2022 and September 30, 2021: March 31, September 30, 2022 2021 (in thousands) Accrued expenses: Accrued pharmaceutical drug manufacturing $ 14,412 $ 8,402 Accrued research and development expenses 2,616 6,062 Accrued payroll and related expenses 2,960 6,094 Accrued professional fees 633 700 Accrued other 1,119 1,171 $ 21,740 $ 22,429 Other long-term liabilities: Uncertain tax positions $ 530 $ 558 Asset retirement obligation 346 — $ 876 $ 558

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	6 Months Ended
	Mar. 31, 2022
Summary of Stock Option Activity Including Performance Based Options	The following table summarizes stock option activity, including performance-based options, for the year-to-date period ending March 31, 2022: Shares Weighted Weighted Aggregate (in thousands) (in years) (in thousands) Outstanding as of September 30, 2021 3,852 $ 48.61 6.4 $ 49,173 Granted 713 73.82 Exercised ( 345 ) 41.26 Forfeited ( 96 ) 67.91 Outstanding as of March 31, 2022 4,124 $ 53.13 6.7 $ 82,997 Options vested and expected to vest as of 4,124 $ 53.13 6.7 $ 82,997 Options exercisable as of March 31, 2022 2,496 $ 47.87 5.2 $ 63,476
Summary of Restricted Stock Unit Activity	The following table summarizes the restricted stock unit activity for the year-to-date period ending March 31, 2022: Restricted Stock Weighted (in thousands, except per share data) Unvested at September 30, 2021 117 $ 43.57 Granted 138 75.33 Vested ( 29 ) 43.57 Cancelled ( 9 ) 57.19 Unvested at March 31, 2022 217 $ 63.15
Stock-Based Compensation Expense	During the three and six months ended March 31, 2022 and 2021 the Company recognized the following stock-based compensation expense: Three Months Ended Six Months Ended March 31, March 31, 2022 2021 2022 2021 (in thousands) Research and development $ 2,710 $ 2,536 $ 5,294 $ 4,955 General and administrative 3,761 2,744 7,239 5,208 $ 6,471 $ 5,280 $ 12,533 $ 10,163 Three Months Ended Six Months Ended March 31, March 31, 2022 2021 2022 2021 (in thousands) Stock options $ 4,962 $ 4,514 $ 9,710 $ 8,863 Performance stock units 79 — 512 — rTSRUs 531 444 823 721 Restricted stock units 899 322 1,488 579 $ 6,471 $ 5,280 $ 12,533 $ 10,163
Performance Share Units and Relative Total Stockholder Return Units [Member]
Summary of PSUs and rTSRUs Activity	The following table summarizes PSU and rTSRU activity for the year-to-date period ending March 31, 2022: PSUs rTSRUs Shares Weighted Shares Weighted (in thousands, except per share data) Unvested at September 30, 2021 111 $ 49.31 111 $ 31.26 Granted 33 77.39 33 54.80 Vested ( 5 ) 61.59 ( 18 ) 40.13 Cancelled ( 27 ) 61.59 ( 14 ) 40.13 Unvested at March 31, 2022 112 54.01 112 $ 35.59

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three and six months ended March 31, 2022 and 2021: Three Months Ended Six Months Ended March 31, March 31, 2022 2021 2022 2021 (in thousands, except per share data) Basic net loss per share: Numerator: Net loss $ ( 33,592 ) $ ( 22,045 ) $ ( 63,707 ) $ ( 30,373 ) Denominator: Weighted average common shares outstanding 20,551 20,171 20,473 20,131 Net loss per share common share—basic $ ( 1.63 ) $ ( 1.09 ) $ ( 3.11 ) $ ( 1.51 ) Diluted net loss per share: Numerator: Net loss $ ( 33,592 ) $ ( 22,045 ) $ ( 63,707 ) $ ( 30,373 ) Denominator: Weighted average common shares outstanding 20,551 20,171 20,473 20,131 Dilutive effect of common stock equivalents — — — — Weighted average common shares outstanding 20,551 20,171 20,473 20,131 Net loss per share common share—diluted $ ( 1.63 ) $ ( 1.09 ) $ ( 3.11 ) $ ( 1.51 ) Anti-dilutive common stock equivalents excluded 3,699 4,268 3,267 4,307

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail)	6 Months Ended
	Mar. 31, 2022
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Entity incorporated, in year	1995

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Assets:
Marketable securities	$ 281,556	$ 295,212
Assets, Fair Value Disclosure, Total	317,912	350,031
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,506	1,506
Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,506	1,506
Level 1 [Member]
Assets:
Assets, Fair Value Disclosure, Total	143,348	137,857
Level 2 [Member]
Assets:
Assets, Fair Value Disclosure, Total	174,564	212,174
Level 3 [Member]
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,506	1,506
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,506	1,506
Money Market Funds [Member]
Assets:
Cash equivalents	36,356
Money Market Funds [Member] | Level 1 [Member]
Assets:
Cash equivalents	36,356	54,819
Corporate Bonds [Member]
Assets:
Marketable securities	108,190	124,703
Corporate Bonds [Member] | Level 2 [Member]
Assets:
Marketable securities	108,190	124,703
Commercial Paper [Member]
Assets:
Marketable securities	66,374	87,471
Commercial Paper [Member] | Level 2 [Member]
Assets:
Marketable securities	66,374	87,471
Assets, Fair Value Disclosure, Total		87,471
U.S. Treasury Notes [Member]
Assets:
Marketable securities	106,992	83,038
U.S. Treasury Notes [Member] | Level 1 [Member]
Assets:
Marketable securities	$ 106,992	$ 83,038

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of the Company's Outstanding Series 1 Nonconvertible Preferred Stock (Detail) - Level 3 [Member] - Series 1 Nonconvertible Preferred Stock [Member]	Mar. 31, 2022	Sep. 30, 2021
Probabilities of Payout [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range	0	0
Probabilities of Payout [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range	65	65
Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range	4.25	4.25

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Values of Outstanding Series 1 Nonconvertible Preferred Stock (Detail) - Series 1 Nonconvertible Preferred Stock [Member]	6 Months Ended
	Mar. 31, 2022USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,506,000
Change in fair value of nonconvertible preferred stock	0
Ending Balance	$ 1,506,000

Marketable Securities - Fair Va

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($)	Mar. 31, 2022	Sep. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 284,209,000	$ 295,210,000
Gross Unrealized Gains	6,000	96,000
Gross Unrealized Losses	(2,659,000)	(94,000)
Fair Value	281,556,000	295,212,000
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	109,901,000	124,678,000
Gross Unrealized Gains	3,000	93,000
Gross Unrealized Losses	(1,714)	(68,000)
Fair Value	108,190,000	124,703,000
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	107,934,000	83,061,000
Gross Unrealized Gains	3,000	3,000
Gross Unrealized Losses	(945,000)	(26,000)
Fair Value	106,992,000	83,038,000
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66,374,000	87,471,000
Gross Unrealized Gains	0
Fair Value	$ 66,374,000	$ 87,471,000

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Long-term marketable securities	$ 42,218	$ 108,416
Maximum [Member] | Short Term Marketable Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year
Long Term Marketable Securities [Member] | Maximum [Member] | Corporate Bonds and U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	3 years
Long Term Marketable Securities [Member] | Minimum [Member] | Corporate Bonds and U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year

Accrued Expenses and Other Lo_3

Accrued Expenses and Other Long-Term Liabilities - Accrued Expenses and Other Current Liabilities as well as Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Accrued expenses:
Accrued research and development expenses	$ 14,412	$ 8,402
Accrued pharmaceutical drug manufacturing	2,616	6,062
Accrued payroll and related expenses	2,960	6,094
Accrued professional fees	633	700
Accrued other	1,119	1,171
Accrued expenses	21,740	22,429
Other long-term liabilities:
Uncertain tax positions	530	558
Asset retirement obligation	346
Other long-term liabilities	$ 876	$ 558

AbbVie Collaboration - Addition

AbbVie Collaboration - Additional Information (Detail) - AbbVie [Member] $ in Thousands	6 Months Ended
	Mar. 31, 2022USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cash consideration received under collaboration from sale of preferred stock, research funding payments, milestone payments and royalties	$ 1,169,000
Collaboration agreement tiered royalty description	from ten percent up to twenty percent, or on a blended basis from ten percent up to the high teens, on the portion of AbbVie’s calendar year net sales

Series 1 Nonconvertible Prefe_2

Series 1 Nonconvertible Preferred Stock - Additional Information (Detail) - Series 1 Nonconvertible Preferred Stock [Member] shares in Thousands	Mar. 31, 2022shares
Class Of Stock [Line Items]
Preferred stock, shares issued	1,930
Preferred stock, shares outstanding	1,930

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity Including Performance Based Options (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2022USD ($)$ / sharesshares	Sep. 30, 2021USD ($)$ / sharesshares
Options
Outstanding as of beginning of period | shares	3,852
Granted | shares	713
Exercised | shares	(345)
Forfeited | shares	(96)
Outstanding as of end of period | shares	4,124	3,852
Options vested and expected to vest as of end of period | shares	4,124
Options exercisable as of end of period | shares	2,496
Weighted Average Exercise Price
Outstanding | $ / shares	$ 48.61
Granted | $ / shares	73.82
Exercised | $ / shares	41.26
Forfeited | $ / shares	67.91
Outstanding | $ / shares	53.13	$ 48.61
Options vested and expected to vest as of end of period | $ / shares	53.13
Options exercisable as of end of period | $ / shares	$ 47.87
Weighted Average Remaining Contractual Term
Outstanding as of end of period	6 years 8 months 12 days	6 years 4 months 24 days
Options vested and expected to vest as of end period	6 years 8 months 12 days
Options exercisable as of end of period	5 years 2 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value | $	$ 82,997	$ 49,173
Options vested and expected to vest as of December 31, 2021 | $	82,997
Options exercisable as of end of period | $	$ 63,476

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) $ in Thousands	6 Months Ended
	Mar. 31, 2022USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate of unrecognized stock-based compensation cost	$ 66,162
Weighted average recognition period	2 years 10 months 24 days
Executive Officers [Member] | Relative Total Stockholder Return Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage	0.00%
Executive Officers [Member] | Relative Total Stockholder Return Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage	150.00%

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of PSUs and rTSRUs Activity (Detail) shares in Thousands	6 Months Ended
	Mar. 31, 2022$ / sharesshares
PSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	111
Granted | shares	33
Vested | shares	(5)
Cancelled | shares	(27)
Unvested, ending balance | shares	112
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 49.31
Weighted Average Grant Date Fair Value, Granted | $ / shares	77.39
Weighted Average Grant Date Fair Value, Vested | $ / shares	61.59
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	61.59
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 54.01
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	111
Granted | shares	33
Vested | shares	(18)
Cancelled | shares	(14)
Unvested, ending balance | shares	112
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 31.26
Weighted Average Grant Date Fair Value, Granted | $ / shares	54.80
Weighted Average Grant Date Fair Value, Vested | $ / shares	40.13
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	40.13
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 35.59

Stock-Based Awards - Summary _3

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member] shares in Thousands	6 Months Ended
	Mar. 31, 2022$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	117
Granted | shares	138
Vested | shares	(29)
Cancelled | shares	(9)
Unvested, ending balance | shares	217
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 43.57
Weighted Average Grant Date Fair Value, Granted | $ / shares	75.33
Weighted Average Grant Date Fair Value, Vested | $ / shares	43.57
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	57.19
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 63.15

Stock-Based Awards - Stock-Base

Stock-Based Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 6,471	$ 5,280	$ 12,533	$ 10,163
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	4,962	4,514	9,710	8,863
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	79	0	512	0
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	531	444	823	721
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	899	322	1,488	579
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,710	2,536	5,294	4,955
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,761	$ 2,744	$ 7,239	$ 5,208

Net Loss Per Share - Basic and

Net Loss Per Share - Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2022	Mar. 31, 2021
Basic net loss per share:
Net loss	$ (33,592)	$ (30,115)	$ (22,045)	$ (8,328)	$ (63,707)	$ (30,373)
Weighted average common shares outstanding —basic	20,551		20,171		20,473	20,131
Net loss per share common share—basic	$ (1.63)		$ (1.09)		$ (3.11)	$ (1.51)
Diluted net loss per share:
Net loss	$ (33,592)	$ (30,115)	$ (22,045)	$ (8,328)	$ (63,707)	$ (30,373)
Basic	20,551		20,171		20,473	20,131
Weighted average common shares outstanding —diluted	20,551		20,171		20,473	20,131
Net loss per share common share—diluted	$ (1.63)		$ (1.09)		$ (3.11)	$ (1.51)
Anti-dilutive common stock equivalents excluded from above	3,699		4,268		3,267	4,307

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income tax benefit	$ 0	$ (7,110,000)	$ 0	$ (10,404,000)
Income tax receivable	$ 28,748,000		$ 28,748,000		$ 37,255,000

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	Nov. 19, 2021USD ($)
Lessee, Lease, Description [Line Items]
Increase in Right of Use Asset and Lease Liability	$ 15,048
500 Arsenal Street, Watertown, Massachusetts [Member]
Lessee, Lease, Description [Line Items]
Lease option to extend	extend the lease term of its existing office and laboratory space at 500 Arsenal Street for an additional 5 years
500 Arsenal Street, Watertown, Massachusetts [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Lease Payment	$ 20,342